IDNA and getnameinfo() and getaddrinfo()

Nicolas Williams Nicolas.Williams at
Mon Jun 14 19:26:31 CEST 2010

Hello, I'm not subscribed to this list, so please Cc' me on replies.

Over in the NFSv4 WG we're discussing how to fix NFSv4.1 to properly
handle IDNA.  In the process of doing so I ran into draft-iab-idn-
encoding, which has a cogent discussion of name service switches
(pictured in figure 2).

draft-iab-idn-encoding aims for Informational status.  I'm wondering if
we could publish a Standards-Track document describing how getnameinfo()
and getaddrinfo() should handle IDNA.

For example, one could say that when using DNS getnameinfo() should:

 - perform the DNS lookup
 - apply ToUnicode() to the resulting domainname
 - attempt to convert the address' name to the caller's locale's codeset
   if that codeset is not UTF-8
    - if failure, then return the A-label as the canonical hostname
    - if success return the U-label (in the caller's locale's codeset)
      as the canonical hostname and the A-label as an alias

And that when using DNS getaddrinfo() should:

 - convert the given host/domainname from the caller's locale's codeset
   to UTF-8 if necessary
 - apply ToASCII(), perform DNS lookups
    - if success, return the IP address(es) found, the given name as the
      canonical hostname, the A-label form of the hostname as an alias,
      and the U-label form (converted to the caller's locale's codeset)
      as an alias if different from the given hostname.

Would you agree?  This would greatly simplify the application of IDNA to
various application protocols, such as, for example, NFSv4.  NFSv4 has
several domainname slots, and several more coming from ancilliary
protocols in current development.  Being able to send un-pre-processed
Unicode in NFS because the peer's getaddrinfo() must handle that
correctly seems like a very good approach -- this way IDNA does not have
to interfere with non-DNS name services.

Unfortunately we probably cannot rely on getnameinfo()/getaddrinfo()
doing the Right Thing.  A Standards-Track RFC on this would probably


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